PREVIOUS: Retrieving a Prior Value of a Field

How to:

Given an aggregated input field and a negative offset, PREVIOUS retrieves the value in a prior row, within a sort break or the entire table. The reset point for the calculation is determined by the value of the PARTITION_ON parameter described in Specify the Partition Size for Simplified Statistical Functions.

Note: The values used in the retrieval depend on the sort sequence (ascending or descending) specified in the request. Be aware that displaying a date or time dimension in descending order may produce different results than those you may expect.

Syntax: How to Retrieve a Prior Value of a Field 

PREVIOUS([prefix.]field, offset)

where:

prefix

Is one of the following optional aggregation operators to apply to the field before using it in the calculation:

  • SUM. which calculates the sum of the field values. SUM is the default value.
  • CNT. which calculates a count of the field values.
  • AVE. which calculates the average of the field values.
  • MIN. which calculates the minimum of the field values.
  • MAX. which calculates the maximum of the field values.
  • FST. which retrieves the first value of the field.
  • LST. which retrieves the last value of the field.
field

Numeric or an alphanumeric field that contains all numeric digits.

The field to be used in the calculation.

offset

Numeric

Is a negative number indicating the number of rows back from the current row to use for the retrieval.

Example: Retrieving a Prior Value of a Field

The following request sets the PARITITON_ON parameter to TABLE and retrieves the value of the QUANTITIY_SOLD field two rows back from the current row. 

SET PARTITION_ON=TABLE
TABLE FILE wflite
SUM QUANTITY_SOLD
COMPUTE PREV = PREVIOUS(QUANTITY_SOLD,-2);
BY PRODUCT_CATEGORY
BY PRODUCT_SUBCATEG
ON TABLE SET PAGE NOLEAD
ON TABLE SET STYLE *
GRID=OFF,$
ENDSTYLE
END

The output is shown in the following image. The value of PREV in the first two rows is zero, as there are no prior rows for retrieval. From then on, each value of PREV is from the QUANTITY_SOLD value from two rows prior, with no reset points.